1. Field of the Invention
This invention relates to a shaft sealing apparatus using a sealing fluid.
2. Prior Art
Typically, a rotating shaft will require support by a bearing surface across which a differential gas pressure is maintained. Leakage across the bearing surface can be avoided in part by using a sealing fluid. According to the prior art, the pressure on the sealing fluid is typically maintained slightly higher than that of a high-pressure gas chamber. The pressure is maintained on a sealing fluid supply chamber so that it prevents the high-pressure gas from leaking into the low-pressure gas chamber across the bearing. Although a certain amount of the sealing fluid supplied into the sealing fluid supply chamber is forced into the high-pressure gas chamber, the greater part of the sealing fluid flows into the low-pressure chamber through a narrow path or clearance between the seal rings and the rotating shaft. This sealing fluid has the function of dissipating the frictional heat caused by the friction of the rotating shaft and the seal ring. On the other hand, some slight part of the sealing fluid flows into the high-pressure side. It generally is necessary to prevent its contact with the gas. In such a case, a substantial amount of the fluid has to be removed at great cost. Accordingly, the pressure of the sealing fluid supply chamber must be necessarily maintained only slightly higher than that of the high-pressure chamber.
However, the disadvantages in shaft sealing apparatus of the prior art which are mentioned above are due to the fact that the pressure in the sealing fluid supply chamber is varied in accordance with changes of pressure in the high-pressure gas chamber. Since the pressure of the sealing fluid supply chamber follows the pressure of the high-pressure gas chamber, the pressure disparity between the pressure of the high-pressure gas chamber and of the sealing fluid chamber is kept constant. Therefore, the amount of the sealing fluid which flows into the low-pressure chamber through the seal rings in the low-pressure side naturally varies. Thus, the cooling effect of the sealing fluid in regard to the frictional heat caused on the slidable contact surface between the low-pressure seal rings and the rotating shaft varies. Accordingly, when the gas pressure of the high-pressure gas chamber becomes extremely low, the pressure of the sealing fluid supply chamber is lowered, and it may happen that the amount of the sealing fluid necessary for cooling the contact surface between the seal rings and the rotating shaft cannot be satisfactorily supplied thereby resulting in excessive heat on the contact surface. Thus, the operation of the bearing must be disturbed by overheating or burning.